This invention relates generally to the control and management of automated manufacturing systems, and more particularly to a system and method for exception handling combining on-line planning and predetermined rules.
Manufacturing systems conventionally require the planning and scheduling of a series of job requests, which may arrive asynchronously over time. A typical manufacturing plant may be represented as a network of transports linking multiple machines, as shown in FIG. 1. A plant may have anywhere from a few to several hundred machines and transports. Unfinished blocks of raw material may enter the plant from multiple sources and completed-jobs can exit at multiple destinations. In the simplified schematic of FIG. 1, Sources 1 and 2 provide materials to Machine 1 and Machine 2, which interface with Machine 3 and Machine 4 as well as Destinations 1 and 2.
Errors in processing in such a system may cause bad objects to flow to the system output. Bad objects are defined as objects that are in some way inconsistent with the expectations at the output, for example, they are out of order in an ordered batch, or they are incorrectly manufactured, positioned, oriented, or otherwise in violation of the original requirements for that object. Such problems are exacerbated in systems with complex processing paths and in systems in which objects from two or more independent jobs are present in the system at the same time. Where exceptions are addressed in existing systems, it is often necessary to dispose of an entire batch currently in production to avoid inconsistent output. Also, such decisions for recovery from failure are often made locally by different modules in the system, in a manner that is opaque to the system-level controller, and thus interfere with optimal decision making by the system-level controller. It is desirable for the system to have a general mechanism for preventing bad output while preserving as much of the good output as possible.